1. Technical Field of the Invention
This invention relates generally to the field of electrical circuits and component design, and more specifically to an improved transistor driver circuit.
2. Background Information and Description of the Related Art (Including Information Disclosed Under 37 CFR xc2xa7xc2xa71.97 and 1.98)
Nearly every household and consumer device manufactured today includes some form of electronic or electromechanical control. Electronics have greatly improved the functionality and convenience of these devices. However, having electronic controls also makes the device susceptible to interference from ambient electromagnetic signals. One goal, then, of good electrical and electronic circuit design is to minimize the magnitude of electromagnetic interference generated, or radiated, by each device. In so doing, the device will become a good neighbor to other electrical and electronic devices in its vicinity.
One field where it is important to minimize the generation of spurious electromagnetic signals is in automotive control systems. Vehicles have a number of sensitive control systems, managing aspects as diverse as engine operation, braking, transmission shifting, navigational tracking and positioning, and extra-vehicle communications. Vehicle manufacturers have strict requirements on electromagnetic (EM) radiation. This is necessary to ensure that one device does not interfere with the operation of a neighboring device.
Certain vehicle control systems present a greater challenge when dealing with radiant EM. These systems include the control of inductive or resistive loads, such as solenoids, coils and relays, that must be switched off and on rapidly. Electronic components commonly referred to as output drivers (low side output drivers or high side output drivers) control the power to such loads. When dealing with control systems that rapidly switch output drivers and their associated driven elements, the amount of radiant EM can be quite high if not managed properly.
This invention relates to a method for reducing electromagnetic radiation from a circuit employing transistor-based output drivers, and more specifically to a method for limiting the load current slew rate and the load voltage slew rate, slew rate being the rate of change of the current or voltage. Examples are given in this application for systems using a high side driver, but the concepts addressed in this patent application are equally applicable to other drive circuits, including low side drivers and H-bridges.
One advantage of the present invention is that the output driver slew rate limits are digitally configurable, allowing the slew rates to be optimized for any given load configuration.
Another advantage of the present invention is that the combination of voltage and current slew rate limiting allows the overall circuit performance to be optimized against radiant electromagnetic energy, more so than could be achieved by employing voltage or current slew rate limiting alone.